J. Patarin

Room-temperature synthesis of silicate mesoporous MCM-41-type materials: influence of the synthesis pH on the porosity of the materials obtained

Pure silica MCM-41 materials were synthesized at room temperature at different pH values ranging from 8.5 to 12. The solids were characterized by XRD, 29Si-MAS-NMR spectroscopy and N2 and Ar adsorption measurements. When the synthesis pH is too high, the degree of polycondensation of the silicate species is too low and, after removal of the organic species by calcination, amorphization occurs. For an intermediate pH value (11), the N2 and Ar adsorption isotherms at 77 K, determined on the corresponding solid, are ‘type I-b like’ and are characteristic of the presence of primary and secondary micropores (d<2 nm). At a low pH value (8.5), a typical MCM-41 material with a mesopore diameter of ~2.6nm is obtained. The adsorption isotherms are of type IV. The influence of the thermal treatment on the as-synthesized samples was studied, and an effect was observed in the material containing micropores. Whereas a short calcination time at 873 K leads to a decrease in the intensity of the XRD peaks, a prolonged calcination time at this temperature leads to an improvement in the degree of organization and to an increase in the total microporous volume of about 18%. This increase can be explained by the greater homogeneity of the micropore surface after such a thermal treatment.

F− mediated synthesis of mesoporous silica with ionic- and non-ionic surfactants. A new templating pathway

Abstract Mesoporous silica precursors were synthesized at room temperature from solutions in the presence of fluoride anions at a pH between 6 and 10 using the cetyltrimethylammonium cation as the surfactant. The solids were obtained from the hydrolysis of SiF62− or mixtures of TMOS and NH4F. When the pH decreases from 10 to 6, the Q4/Q3 ratio increases. This increase is due to the polycondensation of the SiOH groups which is catalyzed by the fluoride anions. Under these conditions, less surfactant S+ is incorporated. The decrease of the number of SiO− groups is partially compensated by the incorporation of F− anions into the neutral framework I0 (S+[I0F−] mechanism). Too high an ionic strength gives rise to low-organized materials. Nevertheless, the increase of the surfactant concentration improves the organization of the materials. By using non-ionic surfactants under similar conditions, the presence of F− enables the formation of materials from reaction mixtures with low silica/surfactant ratios exhibiting characteristics close to those of the material obtained with conventional cationic surfactants.

Pure silica chabazite molecular spring: a structural study on water intrusion-extrusion processes.

Water intrusion-extrusion isotherms performed at room temperature on hydrophobic pure silica chabazite show that the water-Si-CHA system displays real spring behavior. However, differences in pressure-volume diagrams are observed between the first and the other intrusion-extrusion cycles, indicating that some water molecules interact with the inorganic framework after the first intrusion. (29)Si and especially (1)H solid-state NMR showed the creation of new defect sites upon the intrusion-extrusion of water and the existence of two kinds of water molecules trapped in the supercage of Si-CHA: a first layer of water strongly hydrogen bonded with the silanols of the framework and a subsequent layer of liquidlike physisorbed water molecules undergoing interaction with the first layer. This hydrogen bonding scheme is also supported by X-ray powder diffraction.

Synthesis and characterization of high-silica EMT and FAU zeolites prepared in the presence of crown-ethers with either ethylene glycol or 1,3,5-trioxane

Abstract EMT- and FAU-type zeolites were prepared by using a mixture of organic molecules, i.e., crown-ether + ethylene glycol or crown-ether + 1,3,5-trioxane. The products were characterized by elemental analysis, XRD, SEM, thermal analysis, n-hexane adsorption, and n.m.r. spectroscopy. Depending on the method used to prepare the starting gel, the solids obtained showed different characteristics. D.t.a. proved to be a good tool to determine, from the thermal decomposition of the organic templates the presence of structure defects in the EMT and FAU samples.

Synthesis and characterization of 18-crown-6 ether-containing KFI-type zeolite

Pure high silica KFI-type zeolite samples with a framework Si/Al molar ratio as high as 4.0 were prepared by using 18-crown-6 ether as an organic template from a starting aluminosilicate gel containing potassium and strontium cations. The solids were characterized by elemental analysis, SEM, XRD, thermal analysis, solid state n.m.r. spectroscopy, and n-hexane adsorption. The 18-crown-6 ether is occluded in the structure (one molecule/unit cell). Its presence allows reproducible preparations of highly crystalline materials with high Si/Al ratios.

Room-temperature synthesis of crystalline solids in the system ZnOP2O5RH2O, with R being an alkylamine or an alkylammonium ion

Abstract Five novel materials were synthesized at room temperature in the system ZnOP 2 O 5 RH 2 O, where R is an alkylamine or an alkylammonium ion. Three were prepared in presence of 1,4-diazabicyclo[2,2,2]-octane (DABCO), two others were synthesized from reaction mixtures containing tetramethylammonium ions (Me 4 N + ) or hexamethylenetetramine (HMT). The synthesis occurred at room temperature, the starting pH values ranging from 1 to 4. These five solids were characterized by elemental analysis, SEM, XRD, thermal analysis, and solid-state n.m.r, spectroscopy. Contact with water at room temperature for several days leads to a complete transformation of each phase into hopeite. The thermal stability is poor, too; on calcination under air, amorphization or phase transitions occur between 150 and 350°C. According to the observed properties, these new materials probably display an interrupted framework with PO 3 OH or PO 2 (OH) 2 groups.

F-: A MULTIFUNCTIONAL TOOL FOR MICROPOROUS SOLIDS a) MINERALIZING, STRUCTURE DIRECTING AND TEMPLATING EFFECTS IN THE SYNTHESIS

ABSTRACT Three effects may be observed if fluoride anions are present in synthesis mixtures of microporous solids. The first one is a mineralizing (or mobilizing) effect: F allows crystallizing from a gel through a dissolution process. This effect applies especially for silica-based materials which thus may be prepared in media with pH lower than 10-11. The second one is a structure directing effect which means that its presence is necessary to obtain a material with a given structure and/or composition from a given reaction mixture. By this effect three entirely novel materials could be prepared (the silica form of the AST structure type, LTA-GaPO 4 and CLO-GaPO 4 ). The third one is a templating effect: F is incorporated into the framework interstices of the material and contributes strongly to the stabilization of the structure as do the organic template molecules. This effect is chiefly observed when the framework has no charges or if its charges are autocompensated.

Synthesis and structure of the new gallophosphate Mu-6 containing a gallium organic complex as part of the framework

Abstract A new gallophosphate was synthesized in aqueous medium using the macrocycle 1,4,8,11-tetraazacyclotetradecane as organic species. The structure was determined by single crystal X-ray diffraction. The symmetry is monoclinic, space group C2/c, a=0.8842(3)nm, b=1.7781(2)nm, c=1.5805(3)nm, β= 92.05(3)°. The structure consists of gallophosphate chains of gallium-corner-sharing Ga 2 P 2 O 4 four-rings. Each chain is connected to the others via a gallium-organic complex leading to a three dimensional framework. This new gallophosphate shows low thermal stability, a complete amorphization being observed after calcination at 350°C. The results of 13 C and 31 P solid state nmr spectroscopy are in agreement with the structure analysis.

Preparation of silicalite-1/glass fiber composites by one- and two-step hydrothermal syntheses

Abstract The crystallization of silicalite-1 on glass fiber supports by one- and two-step hydrothermal synthesis procedures was investigated. One-step synthesis (130, 150 or 170 °C) provided composites with an overall specific surface area of up to 200 m 2 /g. The effect of the starting composition and synthesis parameters on the physico-chemical properties of the composite was studied. The silicalite-1 content of the composites was controlled by the composition of the starting gel, in particular the tetrapropylammonium hydroxide concentration, the temperature and duration of the synthesis. The substantial increase in the silicalite-1 content of the composites led to a deterioration of the mechanical properties of the fiber support. The application of a two-step procedure, which consists at a rapid crystallisation (150 or 170 °C) after a nucleation at low temperature (130 °C), provided composites with better mechanical properties and surface areas between 26 and 121 m 2 /g. The silicalite-1/glass fiber composites were studied by XRD, SEM, SIMS, TG/DTA and nitrogen adsorption measurements.

Synthesis of mazzite-type zeolites in the presence of organic solvents: study of the structure directing role of p-dioxane

Abstract Syntheses were performed in the system 10SiO 2 :1Al 2 O 3 : x Na 2 O:[ y wt.%organic compound + (100- y )wt.%H 2 O] at 150°C. In the presence of dioxane, for Na 2 O contents between 2 and 3, primarily mazzite-type products were obtained with Si/Al ratios ranging from 3.3 to 4.1. The dioxane content ( y =5–85) influences both the availability of the dioxane-Na + complex, which is essential for MAZ crystallization, and the effective alkalinity. As such, well-crystallized MAZ samples with high and low Si/Al ratios could be obtained at low ( y =5–10) and high dioxane content ( y =85), respectively, while at intermediate content ( y =50), denser phases crystallized. For Na 2 O contents lower than 2, sodalite phases were formed with the neutral dioxane molecule acting as a templating agent, while above 3, mainly gismondine and analcime were produced. For syntheses with high dioxane content, the cyclic ether was partially replaced by other organic solvents (ethers and alcohols) to study the effect of the solvent properties on zeolite crystallization. The solubility of the organic compound in the aqueous phase and its solvating properties toward anions and cations are of key importance with respect to the rate and the type of zeolite synthesis in organic medium.